Whisk 1 tablespoon fish sauce, lemon juice, and 1 tablespoon black pepper together in a bowl until dipping sauce is well mixed.

Heat 2 tablespoons olive oil in a wok or large skillet over high heat; add beef and marinade. Cook and stir beef mixture, 2 tablespoons oyster sauce, and 4 cloves minced garlic together in hot oil until beef is cooked through and sauce begins to thicken, 5 to 10 minutes. Adding garlic over several times during cooking will produce a better mix of flavors.